<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  第一个数：<input type="text" id="num1"><br />
  第二个数：<input type="text" id="num2">
  <p>
    <button onclick="cacl(mul)">相乘</button>
    <button onclick="cacl(div)">相除</button>
  </p>
  <p>
    结果：<input type="text" id="result">
  </p>
  <script>
    function cacl(func) {
      var result = document.getElementById('result')
      var num1 = parseInt(document.getElementById('num1').value)
      var num2 = parseInt(document.getElementById('num2').value)
      if (isNaN(num1) || isNaN(num2)) {
        alert('请输入数字')
      }
      result.value = func(num1, num2)
    }
    function mul(num1, num2) {
      return num1 * num2;
    }
    function div(num1, num2) {
      if (num2 === 0) {
        alert('除数不能为0');
        return '';
      }
      return num1 / num2;
    }
  </script>
</body>

</html>